1. Technical Field
The present invention relates to the filed of organic chemistry, specially, to a chiral aromatic spiroketal bisphosphine ligand, preparation method and use thereof.
2. Background Art
Catalytic asymmetric synthesis is the research hotspot in the field of organic synthesis chemistry (Ohkuma, T.; Kitamura, M.; Noyori, R. 1999, Catalytic asymmetric synthesis. 2nd Ed.). Design and development of excellent chiral ligands and catalyst systems play a central role in asymmetric catalytic synthesis. Because chiral spirane structures (such as chiral aromatic spiroketals) have good rigid structure and formed transition metal complexes have advantages such as high stereoselectivity and chemical selectivity, etc. in asymmetric catalytic reactions, the studies on such ligands have received much attention from organic chemistry researcher (Acc. Chem. Res. 2008, 41, 581; Chem. Asian J. 2009, 4, 32.). In recent years, aromatic spiroketal ligands gradually got attention by people. For example, the complex formed from SPANPhos having benzodihydopyran backbone and metal rhodium showed good catalytic performance in the carbonylation of methanol for preparing formic acid (Angew. Chem. Int. Ed 2003, 42, 1284; Angew. Chem. Int. Ed 2005, 44, 4385). Another bisoxazoline ligand SPANBox having chiral aromatic spiroketal backbone has successfully been applied in asymmetric electrophilic hydroxylation of β-dicarbonyl compound catalyzed by Zn(II) (Chem. Sci. 2011, 2, 1141). However, the synthesis of benzodihydopyran backbone is relatively complicated and the yield is low. Moreover, it is difficult to adjust the backbone. Only racemic backbone can be obtained and further resolution is necessary to obtain optical pure backbone, which is not economic or environmentally friendly.
Chiral aromatic spiroketal is an important structure unit of natural products, bioactive compounds and chiral ligands. Reported methods includes spiroketalization of bisphenol hydroxy-ketone (or analogues) under the catalysis of acids (Tetrahedron Lett. 1998, 39, 5429; J. Chem. Soc., Perkin Trans. 1 2000, 2681; Org. Lett. 2006, 8, 4875; Tetrahedron 2006, 62, 5883; Synthesis 2008, 22, 3605), etherification of benzofuran under halogen (Angew. Chem. Int. Ed. 2001, 40, 4709), intramolecular addition reaction of hydroxy unsaturated bond catalyzed by transition metal (Synlett 2008, 940.), Mitsunobu reaction (Angew. Chem. Int. Ed. 2001, 40, 4713), aromatic Pumerer reaction (Angew. Chem. Int. Ed. 2007, 46, 7458), cycloaddition reaction (J. Org. Chem. 1997, 62, 1058; Org. Lett. 2006, 8, 2365; Tetrahedron Lett. 2006, 47, 3349) and so on. However, these methods are limited to synthesize racemic aromatic spiroketal products. Generally, the resolution of racemic aromatic spiroketal products is necessary to obtain optical pure chiral aromatic spiroketal compounds. The process is complicated and not economic or environmentally friendly.
It is necessary in the art to develop a novel aromatic spiroketal compound and a preparation method for chiral ligand, thereby obtaining racemates or compounds having optocal activity (opitcal pure) through simple reaction to avoid resolution.